396 



Dr. A. Scott. 



[June 16, 



similar to that of those from ordinary air. Fifth, the state of filthi- 

 ness of a sewer seems to have no perceptible effect on the number of 

 micro-organisms. Sixth, the view that the micro-organisms in 

 sewer air chiefly come from outside, is in perfect agreement with 

 what is known as to the distribution of bacteria in air. Seventh, 

 results obtained in the laboratory with an experimental sewer prove 

 that the micro-organisms present in air are diminished to nearly 

 one-half in passing along a moist tube 5 feet long and If inch in 

 diameter at a rate of nearly 1 foot per second. Although most of 

 the micro-organisms in sewer air come from outside, yet there was 

 distinct evidence of their occasional dissemination from the sewage 

 itself. This is the case when splashing occurs, owing to drains 

 entering the sewer at points high up in the roof. It is, therefore, of 

 great importance that drains should be so arranged as to avoid 

 splashing as much as possible. 



In view of the fact that ordinary sewer air is to all appearance 

 comparatively innocent as regards its micro-organisms, experiments 

 were also made to see whether it contained any poisonous volatile 

 base of the nature of a ptomaine. These experiments so far as they 

 went had negative results. 



Experiments as to the efficacy of ordinary water traps in preventing 

 the escape of sewer gas into houses confirmed and extended the results 

 previously obtained by Fergus. 



Though the authors do not discuss the effect of the inhalation of 

 sewer air on health, yet the results of tho above investigation are 

 clearly snch as to make one much more suspicious as to supposed 

 evidence of the bad effects of ordinary sewer air (at least when not 

 vitiated by splashing), such as that examined by them. 



XVIII. "On the Composition of Water by Volume." By 

 Alexander Scott, M.A., D.Sc. Communicated by Lord 

 Hayleigh, D.C.L., Sec. U.S. Received May 23, 1887. 



In 1805 Gay-Lussac and Humboldt published their classical re- 

 searches on the composition of the atmosphere, and to them we are 

 indebted for our knowledge of the proportion by volume in which 

 hydrogen and oxygen combine to form water. Without this know- 

 ledge the determination of the relative densities of the two gases 

 would be of no use in fixing or checking their atomic weights. This 

 is often overlooked, and Avogadro's law taken as absolutely true for 

 these gases at ordinary temperatures and pressures. That this cannot 

 safely be assumed is conclusively proved by the researches of Regnault, 

 Amagat, and others on the effects of change of temperature and pres- 

 sure upon them. Not only do they not follow Boyle's law as usually 



